Wait, do you have low FPS, or server lag? Server lag is a connection issue, and has almost nothing to do with processor/GPU/RAM, but low FPS is due to CPU/GPU/RAM. As far as 'opening up the memory,' do you have other apps running at the same time as WoW? I recommend killing every other app (besides you security stuff), as even IE or FF in the background can eat a big chuck of RAM. Also, There is a memory setting for your addons, click the Addon button in the bottom left corner, and bump that up a bit.
If you have KTM installed, Disable it. On my machine, KTM uses more resources than any other addon by a wide margin. D/L protractor from
http://files.wowace.com to get a profile of how much CPU/RAM your add-ons are using, and disable a few of the bigger ones.
Hope this helps!
-Gritz